Conventionally, a rotary grindstone using glass cloth as a reinforcing material is widely known, but in particular, ones disclosed in Patent Literatures 1 and 2 are known as ones relating to the present invention.
A rotary grindstone disclosed in Patent Literature 1 is one using, as the reinforcing material, a nonwoven fabric of glass cloth having a plurality of warps arranged in parallel, a plurality of first oblique yarns obliquely intersecting the warps, and a plurality of second oblique yarns obliquely intersecting the warps from an opposite direction of the first oblique yarns.
Of course, the nonwoven fabric of the glass cloth is formed by performing impregnation of thermosetting rein to form a prepreg, laying out one sheet of the prepreg in a metal mold, further spreading mixture of abrasive grains with which liquid phenol resin is coated and powdery phenol resin in an even thickness, further stacking a sheet of the prepreg on an upper face of the mixture, and applying pressure from above. That is, the prepregs are arranged on upper and lower faces, and the abrasive grains layer is stacked therebetween so that compression molding is performed.
Next, a rotary grindstone disclosed in Patent Literature 2 will be described.
The rotary grindstone disclosed in the same Literature is a rotary grindstone where two or more layers of glass cloth have been provided inside or a surface of the rotary grindstone as the reinforcing material, wherein weaving directions of respective yarns in the glass cloth intersect each other at an angle of about 45° or 135°.
Therefore, the glass cloth is one manufactured by performing formation to prepregs with methanol-soluble phenol resin, sandwiching abrasive grains between the prepregs, and performing predetermined molding method.